1. Field of the Invention
The present invention relates to the field of electronic fuel control systems for internal combuston engines. More particularly, the present invention relates to that portion of the above noted field which is concerned with direct control of the fuel supply pumping means.
2. Description of the Prior Art
In fuel control systems which provide fuel to reciprocating piston internal combustion engines on an intermittent, or pulse, basis the prior art teaches that the fuel pumps per se are to be energized by a substantially constant level voltage so as to provide fuel to the fuel injector valve means at a fixed, constant pressure and flow rate commensurate with maximum requirements. Typically, these systems provide accumulator means to assist stabilizing fuel pressure with return lines being supplied to return to the fuel reservoir quantities of fuel in excess of that required by the engine. In such systems, it is known that fuel which is recirculated to the vehicle fuel reservoir will contain large amounts of heat which have been picked up from the engine compartment of the vehicle. Such systems usually provide elaborate mechanisms in the reservoir (which is at ambient air temperature) so as to prevent percolation loss of vapor and general increase in the fuel temperature within the fuel tank. One difficulty with an elevated temperature in the fuel reservoir is that hydrocarbon emissions are generated to pollute the atmosphere. An additional problem, of course, is the fact that lost fuel vapors decrease vehicle efficiency and mileage. A further problem with recycling of heated fuel back to the fuel reservoir is the fact that vapor lock situations can occur when heated fuel is drawn into the pump intake and this fuel subsequently vaporizes. It is, therefore, an object of the present invention to provide a control circuit for the fuel pump of such electronic fuel control systems as will permit that pump to operate at the desired fuel flow and pressure rates when necessary for the injection of fuel but which will otherwise not cause fuel to circulate or be pumped.